1. Field of the Invention
The present invention relates in general to a vehicular engine control apparatus, and more particularly to techniques for adjusting the order of implementation of a shifting control of a transmission portion and a control of an engine which would otherwise take place concurrently.
2. Discussion of Prior Art
There is known a hybrid vehicle provided with a plurality of drive power sources. JP-2004-208417A and JP-2005-240918A disclose a such a hybrid vehicle provided with a drive system, which includes a first drive power source in the form of an internal combustion engine and a second drive power source in the form of an electric motor, and which has a drive mode in which the hybrid vehicle is driven with at least the engine held at rest, and a drive mode in which the hybrid vehicle is driven with an operation of the engine. Upon switching the vehicle drive mode between these two drive modes, the engine is controlled to be started or stopped.
The hybrid vehicle as described above may be provided with a transmission which constitutes a part of a power transmitting path. When a control of a shifting action of the transmission (hereinafter referred to as “shifting control”) and a control of the engine (hereinafter referred to as “engine control”) overlap each other or take place concurrently, the shifting control must be implemented according to a change of a vehicle drive force due to the engine control, and therefore tends to be unfavorably complicated.
In view of the above-indicated problem, JP-2004-208417A discloses a technique for initiating the shifting control only after substantial completion of starting of the engine, when the shifting control for a power-on shift-down action of the transmission, for example, and the engine control to start the engine are concurrently required to be implemented.
The technique of inhibiting concurrent implementation of the shifting control and the engine control as disclosed in JP-2004-208417A makes it possible to prevent a shifting shock caused by a variation of a vehicle drive torque due to the shifting control, and a variation of the vehicle drive torque due to the engine control, which variations would otherwise take place concurrently.
The inhibition of the concurrent shifting control and engine control, by initiating the engine control to start the engine only after the completion of the shifting action of the transmission, for example, causes a delayed output of the engine, upon the above-indicated power-on shift-down action taking place as a result of an increase of a vehicle operator's desired vehicle output torque, for instance, which causes starting of the engine. The delayed starting of the engine and an accordingly delayed rise of the vehicle drive force give rise to a risk of deterioration of drivability or acceleration performance of the vehicle as felt by the vehicle operator.
On the other hand, the concurrent shifting control and engine control to improve the acceleration performance of the vehicle gives rise to a risk of complexity of the engine control and deterioration of a starting shock of the engine and the above-indicated shifting shock of the transmission, in a partially or imperfectly shifted state or a neutral state of the transmission in which a vehicle drive force cannot be transmitted through the transmission. In a hybrid vehicle provided with the drive system as disclosed in JP-2005-240918A, for example, the engine control is implemented to start the engine by motoring (cranking) with a first electric motor, and to permit a second electric motor to produce a reaction torque. In the partially shifted or neutral state of the transmission in which a ring gear of the transmission connected to the second electric motor has a small torque or does not have a torque, it is difficult to establish a torque balance of the rotary elements of the transmission in the process of the engine control, resulting in a possibility of deterioration of shocks as a result of the engine control and the shifting control.